Shielding an underwater wellhead hub

ABSTRACT

Method and apparatus for protectively shielding the attachment hub of an underwater wellhead structure. Expansible means, mounted on a support member adapted to be inserted into the bore of an underwater wellhead structure, for shieldingly covering the attachment hub of such structure when the hub is exposed underwater, are installed in the bore before the hub is so exposed.

United States Patent 2,460,561 2/1949 Winkelmann 166/202 X 2,990,851 7/1961 Jackson et al. 166/.5 X 3,050,] 27 8/1962 Foster et al. 166/85 X 3,163,223 12/1964 Bauer et a1 166/.6 X 3,186,488 6/1965 Johnson et al.... l38/89X 3,189,099 6/1965 Otteman et al. 166/75 X 3,428,128 2/1969 Jones 166/181 X 9 3,473,608 10/1969 Castille 166/85 Primary Examiner-Jan A. Calvert AttomeysTimothy L, Burgess, Thomas B. McCulloch,

Melvin F. Fincke, John S. Schneider, Sylvester W. Brock, Jr. and Kurt S. Myers ABSTRACT: Method and apparatus for protectively shielding the attachment hub of an underwater wellhead structure. Expansible means, mounted on a support member adapted to be inserted into the bore of an underwater wellhead structure, for shieldingly covering the attachment hub of such structure when the hub is exposed underwater, are installed in the bore before the hub is so exposed.

PATENTEU M1824 ISYl SHEET 1 BF 3 ATTORNEY.

INVI'QN'I IRS. ROBERT G. MCGLAMERY, THOMAS W. CHILDERS PATENIED AUB24 I971 SHEET 2 [IF 3 FIG. 5.

AT TORNEY.

SHIELDING AN UNDERWATER WELLHEAD HUB BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to apparatus used in connection with the drilling of offshore underwater wells, and more particularly, it pertains to apparatus adapted for use with underwater wellhead equipment.

2. Description of the Prior Art In underwater drilling, where blowout preventers are sealingly connected to hubs on wellhead structure below the surface of the water and usually on the ocean floor, the hub to which the blowout preventer is connected is frequently left naked and unprotected prior to installation of blowout preventer equipment or while blowout preventer equipment is changed. The naked hub can be damaged by objects that have fallen from the drilling vessel or platform or that have broken loose from overhead. A mere scratch of the sealing surface on the hub caused by a fallen object can lead to erosion of the sealed surface during drilling operations. If the object (for example, a piece of cable) is lodged on the hub when the blowout preventer is lowered onto the hub, a cut can be gouged into the sealing surface of the hub. Such damage can lead to a blowout and perhaps loss of the well. At the very least, it can cause several days of downtime to trip the blowout preventer and replace ruined seals. And damage of the sealing surface of the hub of a wellhead structure is not confined to the hub onto which the blowout preventer superstructure is attached, for it can occur to the upper hub of the blowout preventer onto which the marine riser superstructure is connected. However, damage to the hub mounting the blowout preventer has been more acute.

Heretofore, when underwater drilling has been confined to relatively shallow waters (less than about 600 feet), it has been possible to reduce the risk of damage to the hub of wellhead structure by having divers inspect the hub prior to landing and locking blowout preventer equipment onto it. However, this is a costly procedure in terms of rig downtime and diver fees; and it is not errorproof, for objects can still fall onto the hub of the wellhead structure after the inspection trip and before the blowout preventer equipment is landed on the wellhead. Moreover, with the movement of offshore underwater drilling into deep water, diver inspection of the wellhead hub prior to the landing onto it of the blowout preventer becomes impractical, if not physically impossible; yet even greater care in avoiding seal failure between the blowout preventer and wellhead hub has to be exercised in these deep waters, for the capital risk committed is extraordinarily large and the operating margins are very much smaller.

SUMMARY OF THE INVENTION This invention overcomes these problems of underwater drilling by providing method and apparatus for protectively shielding the hub of underwater wellhead structure onto which wellhead superstructure is sealingly attachable while the hub is naked of superstructure and susceptible to damage from falling objects. In accordance with this invention, it has been discovered that this protection can be attained by installing into the bore of an underwater wellhead structure having a hub, before the hub is bared underwater, expansible means which extends outwardly to substantially cover and shield the hub when the hub is free of wellhead superstructure under water, and which moves inwardly of the hub from the position of expansion to permit sealing attachment to the hub of wellhead superstructure run down into that hub.

Shielding apparatus for this protection includes expansible means on one end of a support, the other end of the support being adapted for insertion into the bore of an underwater wellhead structure below the hub of that structure, and coupling means on the support means adapted for coaction with means on a remotely operable tool to releaseably lock the support means to the tool. In a particular aspect of the invention, the expansible means are outwardly moveable to assume an essentially conical configuration for shielding the hub of the wellhead structure. Other aspects of the invention include means on the end of the support means inserted into the bore of the underwater wellhead structure for securing the support means in the wellhead structure, means for equalizing pressures across the aforesaid means for securing the support means in the wellhead structure, and means connected with said support means for resisting cocking of the support means in the wellhead structure.

BRIEF DESCRIPTION OF THE DRAWINGS Several forms which the invention may take are shown in the drawings accompanying and forming part of the present specification. Referring to the drawings:

FIG. 1 is a partial longitudinal sectional view of a shielding apparatus made in accordance with this invention coupled with a remotely operable running tool;

FIG. 2 is a partially stripped-away elevational view of the shielding apparatus of FIG. 1, set in the bore of casing housing which is supported by concentric casing housing of larger diameter, both viewed in longitudinal sections. A blowout preventer attached to the larger diameter casing housing is indicated by outline;

FIG. 3 is an elevational view of FIG. 2, but with the blowout preventer removed;

FIG. 4 is a partial longitudinal sectional view of a portion of the shielding apparatus depicted in FIGS. l-3;

FIG. 5 is an elevational view of another embodiment of the apparatus of the invention;

FIG. 6 is an elevational view, the right half of which is in longitudinal section, of another embodiment of this invention, installed in a wellhead structure carried by a running tool;

FIG. 7 illustrates another method of connecting the wellhead structure of FIG. 6 to a running tool; and

FIG. 8 illustrates a coupling connection of a retrieving tool adapted to be used with the apparatus embodiment of FIGS. 6 and 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The forms shown in the drawings will now be described in detail for the purpose of illustrating how the general principles of the invention may be carried out. FIGS. 6-8 illustrate the use of apparatus constructed in accordance with the invention to protect'the hub of wellhead structure prior to a landing of wellhead superstructure on that hub FIGS. 1-5 depict the employment of apparatus made in accordance with the invention to protect the hub of wellhead structure during a changeover of blowout preventer equipment of a first diameter to blowout preventer equipment of a second smaller diameter. In the drawings, reference numbers applied to an element or part of FIGS. 1-4 are also applied to modifications of that part in FIGS. 5-8, with a single prime mark being affixed to such numbers in FIG. 5 and a double prime mark being affixed to such numbers in FIGS. 6-8.

Referring now to the drawings, reference numerals 10 generally indicate various forms of a shielding apparatus made in accordance with this invention. In each of the illustrated forms of shielding apparatus 10, a support standard 11 mounts an expansible shield 12 at one end. The other end of the support standard is formed into a base 13 or 13 for insertion into the bore of an underwater wellhead structure. Coupling members l4 14' or 14" attached to or formed into the support standard 11 enable the particular shielding apparatus 10 to be run into or retrieved from the hub which it functions to protect, depending on the design requirements associated with the particular protective assignment.

In FIGS. and 6-8, shielding apparatus 10 is illustrated as it appears when being run (FIGS. 1, 6 and 8) or retrieved (FIGS. 1 and 7) from a rig on a floating vessel or other drilling platform. F Or one or both of the running or retrieving operations,

shielding apparatus is releaseably locked by means of the coupling elements 14 (or 14' or 14") with a remotely operable tool 15 (or 15 or 15").

More specifically, in FIG. 1, remotely operable tool 15 is a running and retrieving J tool attached to the lower end of a string of drill pipe 16 being run from the rig (not shown) Coupling elements 14 are comprised of a pair of lugs which extend transversely from the uppermost extension of the support standard 11 (as most advantageouslyviewed in FIGS. 2 and 4) and are adapted to coact with a pair of J slots 17 in the body or mandrel 18 of J" tool 15 in the manner well known to the art, thereby releaseably locking the shielding apparatus 10 to J tool 15. Although the coupling lugs 14 are preferably extended, as depicted, from the uppermost portion of the support standard or sub 11, they may be alternatively formed into the interior of the remotely operable tool 15, in which case the slots 17 in tool 15, with which the lugs coact, are incorporated into the upper portion of support standard 1 1.

A different construction of coupling elements 14' for coacting with a remotely operable retrieving tool 15' is disclosed in FIG. 8, in which shielding apparatus 10 is a tubular member. Coupling elements 14" is formed by an in turned flange 19 having an inwardly inclined outer rim 19a and a downturned, square-shouldered inner rim 19b Flange l9 cooperates with a companionally tapered head 20 unitized to a spring leg 21 hung from the retrieving tool 15 of FIG. 8. The upturned rim 7 22 on the reverse of the tapered side of head 20 is complemensible shield 12 is adapted to be inserted. In addition, each of the expansible shields 12 is inwardly moveable of the hub of the wellhead structure, in which it is supported, by wellhead superstructure attachable to that hub. Advantageously, the configuration which the expansible shields take, when expanded to substantially cover a hub, is essentially conical.

As illustrated in FIGS. 1-4 and 6-8, expansible shield 12 takes the form of a plurality of petals 23, centrally secured to support standard 1 l by any suitable means, such as weldments or a collar, and comprised of circumferentially spaced, outwardly extendable ribs 24, each of which is laterally interconnected with its adjacent member by a flexible webbing 25. The ribs 24 may be made of spring steel biased to assume an expanded position. Alternately, as illustrated in FIGS. l-4, the petals may be urged outwardly by a plurality of bow springs 26 underlying ribs 24. As best seen in FIG. 4, which depicts the bow springs in their unflexed position, springs 26 are fixed at one end to a collar 27 secured to support standard 11 below the point of central attachment of petals 23, while the other ends of the springs 26 are connected to a collar 28 that is longitudinally slidable on the shaft of the support standard 1 1.

Another form of an expansible shield 12 is shown in FIG. 5, in which shield 12 is formed from a fluted metal cone 29, spring biased for outward movement so that its extremities substantially cover and shield the hub of the wellhead structure in which its support standard 11 is inserted. Other expandable movements within the contemplation of this invention, although not depicted, include, for example, an unfurling movement, a spring-loaded hinged movement, or a telescoping rib movement energized and deenergized by remote control.

The expansible shield of the apparatus is placed in the wellhead structure in a constrained, flexed state, before the hub of the wellhead structure is exposed under water. In the case of the blowout preventer changeover illustrated in FIGS. 14,

shielding apparatus 10 is coupled to a remotely operable J tool when being run' into the wellhead structure to be protected. A skirt 30 flaring outwardly from the body or mandrel 18 of the J tool serves to constrain the expansible shield 12 in the flexed, retracted position during running of the apparatus 10 relative to the wellhead structure of concern. The position of the skirt 30 relative to the J slots 17 on the .I tool, and the point of central securement of the petals 23 relative to the lugs 14 on the support standard 1 1 are scaled to assure that the expansible shield is retracted during running. The lugs 14 may be above (FIG. 4) or below, lugs 14" (FIG. 5) the expansible shield 12.

In the case of FIGS. 7 and 8, which illustrate installation of a shielding apparatus 10 to protect wellhead structure prior to landing of a first blowout preventer on that structure, the constraint imposed on the expansible shield 12 during the running of the apparatus 10 is supplied, as is the case with FIGS. l-5, by an adapter 31 made up with a running tool 15a Unlike the J of FIGS. l-S, however, running tool 15a is coupled to a wellhead structure which inturn carries apparatus [0. Accordingly, it is the relative spacing between the adapter 31 and the base 13" of the support standard 11 which assures that he expansible shield 12 is retracted during running.

As explained in greater detail hereinafter in connection with the method of employing the present invention, the disengagement and withdrawal of the running tool 15a (as in the case of FIGS. 7-8) or the wellhead superstructure (as in the case of FIGS. l-5) enables the expansible shield to expand to substantially cover and shieldingly protect the hub of the wellhead structure in which it is installed. Then wellhead superstructure, sealingly attachable to the hub of the underwater wellhead structure protected by the shielding apparatus !10, is run down onto the wellhead structure. As the superstructure is run down onto the hub of the wellhead structure, the inner wall of the wellhead superstructure comes into contact with the extremities of the expansible shield and deflects those extremi ties inwardly of the hub ofthe wellhead structure, as a result of which the landing of the hub of the wellhead superstructure onto the hub of the wellhead structure is unimpeded, yet yet the hub of the wellhead structure has been protected until the last possible moment.

In the retrieval of the shielding apparatus 10 from the wellhead structure after the superstructure has been run down onto the hub of the wellhead structure, it is desirable, in order to conserve service life of the shielding apparatus 10, that there be clearance between the extremities of the expansible shield 12 and the inner wall of the wellhead superstructure. For this purpose, it is preferred that the coupling elements 14, 14' and 14 and the point of central attachment of the expansible shield 12 be spaced on the support standard of the apparatus to permit the extremities of the shield 12 to be urged further inwardly by the skirt on the remotely operable tool employed (for example, skirt 30, and 30' on the J" tool of FIGS. 1-5 and a skirt 32 on the remotely operable retrieving tool 15 of FIG. 8) than the extent to which they were moved inwardly by the wellhead superstructure.

Below expansible shield 12, the lower end of support standard 11 takes a form which permits it to be inserted into the bore of an underwater wellhead structure below the hub of that structure. More specifically, the lower end of the support standard is expanded into base 13, or 13 which is provided with means by which support standard 11 may be secured in the wellhead structure. As illustrated in the drawings, support standardll is expanded into a base 13 or 13' provided with lands 33 or 33' a lower external surface in order that the support standard may be landed on companionally inclined surfaces on the internal wall of the wellhead structure having the wellhead hub tobe protected. Other means by which the base 13 or 13' of the support standard 12 may be secured in a wellhead structure, such as the use of dogs" in a recessed groove in the wellhead to support the base, are familiar to the art of hanging or otherwise supporting casing and the like in well bores and are adaptable to securing apparatus 10 in the wellhead structure of concern. For simplicity of illustration, however, only the use of lands in connectionwith a seat or a bowl in a wellhead structure, such as casing housing, is depicted.

The height of the support standard 11 relative to the lands 33 or 33' is scaled to extend the uppermost end of the support standard sufficiently above the hub of the particular wellhead structure as to allow the extremities of the expansible shield 12 to move outwardly over the hub when freed of constraint. The illustrated movement is arcuately outward. The extent to which the support standard 11 stands above the hub may be less in the case of a radial telescoping finger or rib movement.

In order to equalize pressure across the base 13 or 13 of the support standard 11 when the base is secured within the wellhead structure, pressure equalizing passages 34 or 34 are employed to interconnect the bore of the wellhead structure above and below the base. In the embodiment illustrated in FIGS. 1-4, the base 13 is constructed by threadingly attaching the pin end 35 of a drill pipe sub 36 into the box 37 of a plug 38 having a central passageway 39 which is communicated with ports 40 in the drill pipe sub. In the apparatus of FIG. 5 and FIGS. 6-8,. the passages 34 are formed on the exterior surface of bases 13.

In order to resist cocking of the support standard 11 in the wellhead structure, especially when the when the base 13 or 13' is secured in the wellhead structure by means of lands 33 or- 33, the measure is taken of surrounding the support standard with a brace which is shaped, relative to the internal configuration of the bore of the wellhead structure, to prevent the undesired cocking. The uppermost extension of the brace does not lie above the hub of the wellhead structure, and is longitudinally spaced from the hub sufficiently to allow the extremities of the expansible shield 12 to expand outwardly over the hub when the constraint of a remotely operated running tool (or 15 or 15a) is removed. In the embodiment depicted in FIGS. 1 and 2, bracing of the support standard 11 is provided by threadingly attaching a cylindrical sleeve 41 onto the upper perimeter of plug 38 concentric to the support standard (drill pipe sub 36). In the embodiment shown in FIG. 5,

base 13 is itself formed into a cylindrical brace of height sufficient to resist cocking of the support standard 11 in the wellhead.

A braced, pressure-relieving support 11 is, therefore, secured in the bore of a wellhead structure to enable an expansible shield 12 to expand to substantially cover and protectively shield the hub of the wellhead structure from objects overhead. Preferably, the configuration whichthe expansible shield takes on expansion is conical, since this shape suitably deflects rather than lodges falling objects.

METHODOLOGY OF THE INVENTION In accordance with the invention, the hub of an underwater wellhead structure having a bore surrounded by the hub is protectively shielded by installing into the bore, before the hub is exposed under water, an expansible device which expands to substantially cover and protectively shield the hub when the hub is subsequently exposed under water. More specifically, the wellhead structure may be an underwater wellhead terminating in a casing housing having a hub, in which case the wellhead super structure sealingly attachable on the hub of that casing housing is a blowout preventer. In another application of the invention, the underwater wellhead structure is a blowout preventer mounted on the casing housshield the upper hub of .a blowout preventer until installation of a marine riser onto the blowout preventer.

In FIG. 7, the remotely operable running tool 15a has a left- I hand thread on the lower external surface of that tool's skirt 51. Thread 50 is threadingly connected to the upper interior wall of a 20-inch casing housing 52 made up on the joint of a 20-inch casing string 53 which extends downwardly to a 30-inch conductor pipe 54 (not illustrated in FIG. 7, but viewable in FIG. 6). Running tool 15a is inturn made up on the lowermost extension of a drill pipe string 16 and interconnects string 16 and a drill pipe stinger string 55. Drill pipe stinger string 55 extends downwardly through the ZO-inch casing string 53 and is used to cement the 20-inch casing string to the 30-inch conductor pipe in subsequent operations. Surrounding drill pipe stinger 55 and supported by lands 33 set on inclined sealing surfaces 56 of ZO-inch casing housing 52 is the tubular shielding apparatus 10 hereinbefore described. The expansible shield 12 of the shield apparatus 10 is constrained from expansion by the skirt 51 of tool 15a. The cylindrical shape of the base 13' conforms to the configuration of the internal wall of casing housing 52 to brace apparatus 10 upright between drill string 55 and casing housing 52.

A different running too] 15a is illustrated in FIG. 6, which also depicts casing housing 52 seated in the bowl 57 of a 30- inch conductor housing 58. In FIG. 6, the 20-inch casing housing 52 is releaseably locked to a 20%-inch collet connector 59 made up onto a 20%-inch collet connector adapter 31 threaded onto drill pipe string 16. Such a collet connector is illustrated on page 1248 of the Composite catalogue of Oil Field Equipment and Services, 1966-1967, published by Gulf Publishing Company, Houston, Texas. A skirt 60 on the 20%- inch collet connector adapter 31 constrains the expansible shield 12 and'also terminates in a hub which the 20%-inch collet connector 59 to the hub 61 of the 20-inch casing housing.

Using either of the running tools 15a of FIG. 6 or FIG. 7, the 20-inch casing housing 52 is landed in the 30-inch conductor pipe housing 58 and cementing operations are conducted down through the drill pipe and drill pipe stinger. After cementing is completed, the collet connector 59 of FIG. 6 is disengaged from hub 61 by tripping locking dogs 62, or the lefthand threaded running tool of FIG. 7 is turned to the right three times, both of which operations are familiar to the art, and the running tool 15a is withdrawn from 20-inch casing housing 52 and its hub 61. The withdrawal of the running tool 150 releases the constraint imposed on the expansible shield 12 by the skirt of the running tool, allowing expansible shield 12 to expand so that its extremities substantially cover and shieldingly protect hub 61 when hub 61 is first bared or exposed to the water.

After running tool 15a has been withdrawn, a 20%-inch blowout preventer superstructure 63, sealingly attachable, as by a collet connector 64, to the hub 61 ofthe 20-inch casing housing, is rundown onto hub 61 in the manner known to the art. (Blowout preventer 63 and collet connector 64 are depicted in shadow in FIG. 2.) As 20%-inch blowout preventer 'sealingly attached, to hub 61, shielding apparatus 10 is removed from the ZO-inch casing housing.

Referring to FIG. 8, a retrieving tool 15 is run down through the bore of blowout preventer superstructure 63 until tapered head 20 has passed through the coupling aperture of the sleeved shielding apparatus 10 to releaseably lock the coupling flange 19 of the shielding apparatus to the retrieved tool 15". After the retrieving tool 15" is coupled with the sleeved shielding apparatus 10, it 15" withdrawn upward through the superstructure to the drilling platform for release by lifting drill string 16.

The above operation for shielding hub 61 of the 20-inch casing housing prior to installation of blowout preventer 63, and the method of installing blowout preventer 63 while protecting hub 61 are applicable for protecting the upper hub of the blowout preventer 63 prior to installation of the marine riser (not shown) on preventer-'63 and for installation of the marine riser on the protected hub.

Referring now to FIG. 2, drilling has progressed to the setting in and installing of l3%-inch casing 65, the upper joint of which is made up in a 13% casing housing 66 which is seated in the bowl of the 20-inch casing housing 52, with which it is concentric. Cementing operations have been conducted to cement the 13% casing 65 in the 20-inch casing 52, and a smaller sized blowout preventer is to be installed on the hub 67 of the l3%-inch casing housing 66. Before this is done, however, the 20% blowout preventer must be detached from the hub 61 of the ZO-inch housing and retrieved.

In order to protectively shield the hub 67 of the 13% casing housing during removal of blowout preventer 63 from the 20- inch casing housing 52, a shielding apparatus 10 such as illustrated in FIGS. l-S is run into the bore of the 13%-inch casing housing '66 with the remotely operable running J tool 15. While the shielding ap aratus 10 is being run down into place, the skirt 30 of the J" tool constrains the expansible shield 12 of the apparatus in a flexed state, as depicted in FIG. 1.

After the shielding apparatus 10 is run into the bore of 13%- inch casing housing 66 and seated in the bowl of that casing housing on its lands 33, the J tool 15 is disengaged with a jaying movement off the coupling lugs 14 and pulled up toward the drilling platform. As the J tool is withdrawn from the shielding apparatus 10, the skirt 30 ofthe .l is lifted off the expansible shield 12. On release of the constraint imposed by the skirt 30 of the running tool 15, the expansible shield 12 expands to contact the inner wall of the blowout preventer 63.

After the J" tool is lifted, the lower flange or hub of blowout preventer 63 is unlocked from hub 61 of the 20-inch casing housing by actuation of the locking dogs on collet connector 64, and blowout preventer 63 is retrieved to the surface. As the lowermost inner portion of blowout preventer 63 rises past and clears the extremities of expansible shield 12, expansible shield 12 will expand to a position allowing its extremities to substantially cover and shieldingly protect the hub 67 of the l3%-inch casing housing when hub 67 is first exposed to the water. FIG. 3 illustrates a protective shield which shielding apparatus 10 provides the l3%-inch hub whenit is exposed to the water. 1

Then, in an operation identical to the landing and locking of the ZOili-inch blowout preventer onto the 20-inch casing housing hub, the l3%-inch blowout preventer (not illustrated) is run down onto the hub of the 13%-inch casing housing 66 to urge the expansible shield 12 inwardly of the hub 67,. and the l3%-inch blowout preventer is sealingly attached to the hub of the l3%-inch casing housing. Then the J tool 15 of FIGS. 1-2 (or .l" tool 15' of FIG. 5, if the shielding apparatus of FIG. 5 is employed) is rundown through the l3%-inch blowout preventer and jayed onto the coupling lugs of the shielding apparatus to releaseably lock onto the apparatus to the J tool, subsequent to which the shielding apparatus 10 is retrieved from the l3%-inch casing housing.

Thus, it is apparent that the present invention solves the problem of protecting the exposed hub of underwater wellhead structure and overcomes the difficulties associated with using divers to inspect the hub, particularly if the drilling of the well is being conducted in deep waters.

At all times that the hub of concern is brought into contact with water. the present method and apparatus provide ways and means to protect it from overhead objects. Of course, the illustrations and description of the embodiments of the invention are merely exemplary of apparatus employable to achieve the ends the invention encompasses. It is manifest that other embodiments or improvements may be employed without departing from the spirit and scope of the invention defined in the subsequent claims.

What is claimed is:

1. A shielding apparatus adapted for use in an underwater wellhead structure having a hub surrounding a bore comprismg:

a. support means having first and second ends, the second end being adapted for insertion into the bore of an underwater wellhead structure below the hub thereof;

b. expansible shielding means secured to the first end of said support means and expandable to extend over said hub for shielding, when expanded, the upper end of said hub of said wellhead structure, and compressible to a position inwardly of said bore; and

c. coupling means on said support means adapted to coact withmeans on a remotely operable tool to releasably lock said support means to said tool; and

d. securing means on said second end of said support means for securing said support means in said wellhead structure, whereby the expansible means will be positioned above the topof said hub when so secured.

2. The apparatus of claim 1 further comprised of means for equalizing pressure levels across said securing means on said second end.

3. The apparatus of claim 1 in which said support means further comprises means for resisting cocking of the support means in the wellhead structure.

4. The apparatus of claim I in which said expansible means is outwardly expandable to a generally conical configuration which substantially covers and protectively shields said hub.

5. The apparatus of claim 1 in which said coupling means is positioned on said support means to allow said expansible means to be urged inwardly of said hub by said too.

6. The apparatus of claim 1 in which said expansible means comprises:

outwardly biased means inwardly attached to said support means for outward extension to said position outside said support means on release of constraint imposed thereupon.

7. The apparatus of claim 1 in which said expansible means comprises rib means centrally attached to said support means and interconnected by web means for arcuately outward extension to said position outside said support means, and

spring means operatively associated with said rib means to urge said rib means to said position on release of constraint imposed on said rib means.

8. A shielding apparatus adapted for use in an underwater wellhead structure having a hub surrounding a bore, comprised of:

a. elongated support means having first and second ends;

b. expansible shielding means secured to the first end of said support means and outwardly expandable to extend over said hub for shielding, when expanded, the upper end of said hub of said wellhead structure, and which is compressible to a position inwardly of said bore;

0. landing means on said second end of said support means for landing said support means in the bore of said wellhead structure so that said first end extends above said hub sufficiently to permit said expansible shielding means to expand'to said configuration;

d. means connected to said support means above said landing means and shaped relative to the configuration of said bore to resist cocking of the landing means in said wellhead structure;

e. passage means in said support means for equalizing said pressure across said landing means; coupling means connected to said support means adapted to coact with means in a remotely operable tool tb releaseably lock said support means to said tool, said coupling means being in a position to allow said expansible means to be urged inwardly of said hub by said tool.

9. The apparatus of claim 8 in which said expansible shielding means comprises:

outwardly biased means inwardly attached to said support means for outward extension, on release of imposed constraint, to a generally conical configuration which sub stantially covers and protectively shields said upper end of said hub 10. A shielding apparatus for protection of an underwater wellhead structure having a hub surrounding a bore, comprismg:

a. an elongated standard having a base adapted to be secured within a wellhead structure below said hub so that the upper end of said standard is above said hub;

b. passage means across said base of said standard adapted to interconnect the bore of said wellhead structure above and below said base when said base is secured in said wellhead structure;

c. sleeve means surrounding said standard and secured at one end to said base, the other end of said sleeve means terminating below the upper end of said standard;

d. coupling means connected to the upward end of said standard for releaseably coacting with a remotely opera ble tool; and 4 e. expansible shield mounted on the upper end of said standard below said coupling means so as to extend over said hub when expanded, including e, rib means centrally attached to said support means and interconnected by web means for arcuately outward extension to said position outside said support means,and e spring means operatively associated with said rib means to urge said rib means to said position on release of constraint imposed on said rib means. 11. A method of installing a superstructure sealingly attachable to the hub of an underwater wellhead structure extending upwardly in a hub which surrounds a bore, said wellhead structure carrying in said bore shielding means including expansible means expanded to substantially cover and shieldingly protect said hub, comprising a. running said superstructure down onto said hub of said wellhead structure to compress said expansible means inwardly of said hub, b. removing said shielding means from said wellhead structure by b running a retrieving tool, capable of releaseably locking with coacting coupling means associated with said shielding means, down through said superstructure to releaseably lock said shielding means to said retrieving tool, and

b withdrawing said retrieving tool upwardly through said superstructure.

12. The method of claim 11 in which said underwater wellhead structure is an underwater wellhead terminating in a casing housing having said hub and said superstructure sealingly attachable on said hub is a blowout preventer sealingly attachable on said casing housing.

13. The method of claim 11 in which said underwater wellhead structure is a blowout preventer and said superstructure sealingly attachable on said hub is a marine riser.

M. In a method of removing a first blowout preventer sealingly attached to a first casing housing which concentrically supports a second casing housing having a hub surrounding a bore. the improvement of protectably shielding the hub of the second casing housing during removal of the first blowout preventer from the first casing housing, comprising:

a. running shielding means including expansible means into the bore of said second casing with a running tool while maintaining said expansible means in a constrained, flexed state;

b. disengaging and withdrawing said running tool from said shielding means, said expansible means on release of the constraint imposed by said running tool expanding to contact the inner wall of said blowout preventer, and

c. retrieving said first blowout preventer to allow said expansible means to expand so that its extremities substantially cover and shieldingly protect said hub.

15. In the underwater drilling of a well, in which a first blowout preventer sealingly attached to a first casing housing is removed and a second blowout preventer is subsequently sealingly installed on a second casing housing concentrically supported within said first casing housing, said second casing housing having a hub surrounding a bore, the improvement of protectively shielding the hub of the second casing housing during the removal of the first blowout preventer and the installation of the second blowout preventer, comprising the sequential steps of:

a. running shielding means including expansible means into the bore of said second casing with a running tool so that said expansible means extends above said hub, while maintaining said expansible means in a constrained, flexed state;

b. disengaging and withdrawing said running tool from said shielding means, said expansible means on release of the contraint imposed by said running tool expanding to contact the inner wall of said first blowout preventer;

c. retrieving said first blowout preventer to allow said expansible means to expand so that its extremities substantially cover and shieldingly protect said hub;

(1. running said second blowout preventer down onto the hub of said second casing housing to urge said expansible means inwardly of said hub;

e. sealingly attaching said second blowout preventer to said hub;

f. running a retrieving tool, capable of coating with coupling means associated with said shielding means, down through said second blowout preventer to releaseably lock said shielding means to said retrieving tool, and

g. retrieving said shielding means from said second casing housing.

16. In an underwater wellhead structure having a hub surrounding a bore, a shielding apparatus comprising:

a support means having first and second ends, the second end having securing means thereon for coacting with means in said wellhead structure to secure said support means in said wellhead structure;

b. expansible means secured to the first end of said support means and positioned above the top of said hub when said .support means is secured in said wellhead structure, said expansible means being compressible to a position inwardly of said bore and expandable to extend over said hub for shielding, when expanded, the upper end of said hub of said wellhead structure; and

c. coupling means on said support means adapted to coact with means on a remotely operably tool to releasably lock said support means to said tool.

17. Tl-le shielding apparatus of claim 16 further comprising:

means connected to said support means shaped relative to the configuration of said bore to resist cocking of the sup port means in the wellhead structure.

18. The shielding apparatus of claim 16 further comprising: passage means in said support means for equalizing the pressure across said securing means on said second end. 19. in an underwater wellhead structure having a hub surrounding a bore, a shielding apparatus comprising:

a. support means having first and second ends, said second end having secured means thereon for coacting with means in said wellhead structure to secure said support means in said wellhead structure;

b. expansible means secured to the first end of said support means and positioned above the top of said hub when said support means is secured in said wellhead structure, said expansible means including means biased outwardly to extend, on release of imposed constraint, to a generally conical configuration which substantially covers and protectively shields said upper end of said hub;

c. coupling means on said support means adapted to coact withmeans on a remotely operable tool to releaseably lock said support means to said tool;

d means connected to said support means shaped relative to the configuration of said bore to resist cocking of the support means in the wellhead structure; and

e. passage means in said support means for equalizing the pressure across said securing means on said second end.

20. A method of protectively shielding the hub of an underwater wellhead structure having a bore which the hub surrounds, comprising:

installing in said bore, before said hub is exposed under water, shielding means including constrained expansible means compressible to a position inwardly of said bore for shielding, when expanded, the upper end of said hub of said wellhead structure;

removing constraint from said expansible means; and

exposing said hub under waterv v 21. A method of protectively shielding the hub of an untachable to said hub, comprising:

a. running said wellhead structure into position with a running too], said wellhead structure carrying shielding means including expansible means in said bore for shielding said hub when said running tool is disengaged and withdrawn from said structure, and

b. disengaging and withdrawing said running tool from said wellhead structure to allow said expansible means to expand to substantially cover and shieldingly protect said hub.

22. The method of claim 21 in which said underwater wellhead structure is an underwater wellhead terminating in a casing housing having a hub.

23. The method of claim 21 in which said underwater wellhead structure is a-blowout preventer. 

1. A shielding apparatus adapted for use in an underwater wellhead structure having a hub surrounding a bore comprising: a. support means having first and second ends, the second end being adapted for insertion into the bore of an underwater wellhead structure below the hub thereof; b. expansible shielding means secured to the first end of said support means and expandable to extend over said hub for shielding, when expanded, the upper end of said hub of said wellhead structure, and compressible to a position inwarDly of said bore; and c. coupling means on said support means adapted to coact with means on a remotely operable tool to releasably lock said support means to said tool; and d. securing means on said second end of said support means for securing said support means in said wellhead structure, whereby the expansible means will be positioned above the top of said hub when so secured.
 2. The apparatus of claim 1 further comprised of means for equalizing pressure levels across said securing means on said second end.
 3. The apparatus of claim 1 in which said support means further comprises means for resisting cocking of the support means in the wellhead structure.
 4. The apparatus of claim 1 in which said expansible means is outwardly expandable to a generally conical configuration which substantially covers and protectively shields said hub.
 5. The apparatus of claim 1 in which said coupling means is positioned on said support means to allow said expansible means to be urged inwardly of said hub by said too.
 6. The apparatus of claim 1 in which said expansible means comprises: outwardly biased means inwardly attached to said support means for outward extension to said position outside said support means on release of constraint imposed thereupon.
 7. The apparatus of claim 1 in which said expansible means comprises rib means centrally attached to said support means and interconnected by web means for arcuately outward extension to said position outside said support means, and spring means operatively associated with said rib means to urge said rib means to said position on release of constraint imposed on said rib means.
 8. A shielding apparatus adapted for use in an underwater wellhead structure having a hub surrounding a bore, comprised of: a. elongated support means having first and second ends; b. expansible shielding means secured to the first end of said support means and outwardly expandable to extend over said hub for shielding, when expanded, the upper end of said hub of said wellhead structure, and which is compressible to a position inwardly of said bore; c. landing means on said second end of said support means for landing said support means in the bore of said wellhead structure so that said first end extends above said hub sufficiently to permit said expansible shielding means to expand to said configuration; d. means connected to said support means above said landing means and shaped relative to the configuration of said bore to resist cocking of the landing means in said wellhead structure; e. passage means in said support means for equalizing said pressure across said landing means; f. coupling means connected to said support means adapted to coact with means in a remotely operable tool to releaseably lock said support means to said tool, said coupling means being in a position to allow said expansible means to be urged inwardly of said hub by said tool.
 9. The apparatus of claim 8 in which said expansible shielding means comprises: outwardly biased means inwardly attached to said support means for outward extension, on release of imposed constraint, to a generally conical configuration which substantially covers and protectively shields said upper end of said hub.
 10. A shielding apparatus for protection of an underwater wellhead structure having a hub surrounding a bore, comprising: a. an elongated standard having a base adapted to be secured within a wellhead structure below said hub so that the upper end of said standard is above said hub; b. passage means across said base of said standard adapted to interconnect the bore of said wellhead structure above and below said base when said base is secured in said wellhead structure; c. sleeve means surrounding said standard and secured at one end to said base, the other end of said sleeve means terminating below the upper end of said standard; d. coupling means connected to the upward end of said standarD for releaseably coacting with a remotely operable tool; and e. expansible shield mounted on the upper end of said standard below said coupling means so as to extend over said hub when expanded, including e1. rib means centrally attached to said support means and interconnected by web means for arcuately outward extension to said position outside said support means, and e2. spring means operatively associated with said rib means to urge said rib means to said position on release of constraint imposed on said rib means.
 11. A method of installing a superstructure sealingly attachable to the hub of an underwater wellhead structure extending upwardly in a hub which surrounds a bore, said wellhead structure carrying in said bore shielding means including expansible means expanded to substantially cover and shieldingly protect said hub, comprising a. running said superstructure down onto said hub of said wellhead structure to compress said expansible means inwardly of said hub, b. removing said shielding means from said wellhead structure by b1. running a retrieving tool, capable of releaseably locking with coacting coupling means associated with said shielding means, down through said superstructure to releaseably lock said shielding means to said retrieving tool, and b2. withdrawing said retrieving tool upwardly through said superstructure.
 12. The method of claim 11 in which said underwater wellhead structure is an underwater wellhead terminating in a casing housing having said hub and said superstructure sealingly attachable on said hub is a blowout preventer sealingly attachable on said casing housing.
 13. The method of claim 11 in which said underwater wellhead structure is a blowout preventer and said superstructure sealingly attachable on said hub is a marine riser.
 14. In a method of removing a first blowout preventer sealingly attached to a first casing housing which concentrically supports a second casing housing having a hub surrounding a bore, the improvement of protectably shielding the hub of the second casing housing during removal of the first blowout preventer from the first casing housing, comprising: a. running shielding means including expansible means into the bore of said second casing with a running tool while maintaining said expansible means in a constrained, flexed state; b. disengaging and withdrawing said running tool from said shielding means, said expansible means on release of the constraint imposed by said running tool expanding to contact the inner wall of said blowout preventer, and c. retrieving said first blowout preventer to allow said expansible means to expand so that its extremities substantially cover and shieldingly protect said hub.
 15. In the underwater drilling of a well, in which a first blowout preventer sealingly attached to a first casing housing is removed and a second blowout preventer is subsequently sealingly installed on a second casing housing concentrically supported within said first casing housing, said second casing housing having a hub surrounding a bore, the improvement of protectively shielding the hub of the second casing housing during the removal of the first blowout preventer and the installation of the second blowout preventer, comprising the sequential steps of: a. running shielding means including expansible means into the bore of said second casing with a running tool so that said expansible means extends above said hub, while maintaining said expansible means in a constrained, flexed state; b. disengaging and withdrawing said running tool from said shielding means, said expansible means on release of the contraint imposed by said running tool expanding to contact the inner wall of said first blowout preventer; c. retrieving said first blowout preventer to allow said expansible means to expand so that its extremities substantially cover and shieldingly protect said hub; d. runnIng said second blowout preventer down onto the hub of said second casing housing to urge said expansible means inwardly of said hub; e. sealingly attaching said second blowout preventer to said hub; f. running a retrieving tool, capable of coating with coupling means associated with said shielding means, down through said second blowout preventer to releaseably lock said shielding means to said retrieving tool, and g. retrieving said shielding means from said second casing housing.
 16. In an underwater wellhead structure having a hub surrounding a bore, a shielding apparatus comprising: a. support means having first and second ends, the second end having securing means thereon for coacting with means in said wellhead structure to secure said support means in said wellhead structure; b. expansible means secured to the first end of said support means and positioned above the top of said hub when said support means is secured in said wellhead structure, said expansible means being compressible to a position inwardly of said bore and expandable to extend over said hub for shielding, when expanded, the upper end of said hub of said wellhead structure; and c. coupling means on said support means adapted to coact with means on a remotely operably tool to releasably lock said support means to said tool.
 17. THe shielding apparatus of claim 16 further comprising: means connected to said support means shaped relative to the configuration of said bore to resist cocking of the support means in the wellhead structure.
 18. The shielding apparatus of claim 16 further comprising: passage means in said support means for equalizing the pressure across said securing means on said second end.
 19. In an underwater wellhead structure having a hub surrounding a bore, a shielding apparatus comprising: a. support means having first and second ends, said second end having secured means thereon for coacting with means in said wellhead structure to secure said support means in said wellhead structure; b. expansible means secured to the first end of said support means and positioned above the top of said hub when said support means is secured in said wellhead structure, said expansible means including means biased outwardly to extend, on release of imposed constraint, to a generally conical configuration which substantially covers and protectively shields said upper end of said hub; c. coupling means on said support means adapted to coact with means on a remotely operable tool to releaseably lock said support means to said tool; d. means connected to said support means shaped relative to the configuration of said bore to resist cocking of the support means in the wellhead structure; and e. passage means in said support means for equalizing the pressure across said securing means on said second end.
 20. A method of protectively shielding the hub of an underwater wellhead structure having a bore which the hub surrounds, comprising: installing in said bore, before said hub is exposed under water, shielding means including constrained expansible means compressible to a position inwardly of said bore for shielding, when expanded, the upper end of said hub of said wellhead structure; removing constraint from said expansible means; and exposing said hub under water.
 21. A method of protectively shielding the hub of an underwater wellhead structure having a bore which the hub surrounds, prior to installation of superstructure sealingly attachable to said hub, comprising: a. running said wellhead structure into position with a running tool, said wellhead structure carrying shielding means including expansible means in said bore for shielding said hub when said running tool is disengaged and withdrawn from said structure, and b. disengaging and withdrawing said running tool from said wellhead structure to allow said expansible means to expand to substantially cover and shieldingly protect said hub.
 22. The method of claim 21 in which said underwater wellhead structure is an underwater wellhead terminating in a casing housing having a hub.
 23. The method of claim 21 in which said underwater wellhead structure is a blowout preventer. 